Well sonic, You could try making a Mind control defence. Heres the Catch. When i say mind control defence you think of mind COntrolling. Your should make it so that your can an Archon and you Mind Control the enemy. Or you could make it so you Mc say a Ling and it will SHoot and Observer and you have to kill as many as possible. Make it a 4 player game. If you choose to do this, Make sure you make the terrain look nice

. I'm sorry if this isn't good enough its just what came to mind.
You could always make a new Version of Splash Defence. Its not that hard.